I think you need to explain a little more of the desired effect. For example: what modules have you installed? How do you know how much food was spent? Where do you get it from? What representation is there in Odoo for this process?

This is a simple production process. You should use the MRP module to describe the process properly. You have raw material (small shrimps or eggs or whatsoever), you have work centers (ponds) and you have feed, which is also a raw material. You have a cycle time (production time). So just set up your Bill of Materials, your work orders and your resources properly, and you can track whatever you want, see https://www.odoo.com/page/manufacturing as a teaser.

What would be the reason not to use the sale module for both the actual sales as well as the food sales? Also, what is the concrete problem you are running in on? I am pretty sure projects such as these can be done, but someone who knows the business well enough should create a plan and/or analysis on the current situation. Maybe there is an Odoo partner located near you?